1. The Field of the Invention
This invention relates to the disinfection of water and, more particularly, to improved methods and apparatus for treating water with ozone. It will be understood that the disinfection of water refers to processes in which pathogenic organisms present in water are killed to prevent the propagation of water-borne diseases.
It is well known that the demands for potable water supplies have grown enormously in the past several decades. Not only has it become difficult to find new sources of water, but also, the existing supplies of ground and surface water have become polluted by industrial and domestic wastes. As a consequence, the necessary treatment of water required to insure the removal of domestic and industrial wastes, chemicals, odors, and pathogenic organisms has become a complex art. With increased pollution, larger dosages of chemicals, most commonly chlorine, are required to achieve the desired level of disinfection. Unfortunately, chlorine imparts a distinct unpleasant taste and smell to water which cannot economically be removed in processing. When highly chlorinated, the water not only tastes bad by itself but also its unpleasant character permeates foods cooked in it and imparts a rather medicinal flavor to beverages made from it, such as coffee and tea.
To meet the rising demand for potable water that is free from objectionable odors and tastes, it has become a common practice to bottle water obtained from uncontaminated sources and use this bottled water for drinking and cooking. Even when this water is obtained from springs or wells in rural areas where the ground water is substantiallY free from industrial and domestic wastes, it is frequently necessary to disinfect the water to reduce pathogenic organisms to safe levels as required by various governmental agencies. It is at once obvious that if chlorine is used as the disinfectant, the primary purpose of preparing bottled water will be nullified.
For the above reasons it is important in bottling water to provide methods for the disinfection of water that will not impart a characteristic odor or taste to the water. Such methods include, for example, treatment with ultraviolet rays, heating, boiling or distilling, treatment with ozone, and other methods. This invention, however, is concerned only with the disinfection of water by treatment with ozone.
Ozone treatment is preferred in preparing potable bottled water since ozone is a strong disinfectant that is effective in destroying pathogenic organisms; ozone is a strong oxidizing agent that removes colors, odors and tastes from the water; ozone is comparatively inexpensive; and most importantly, ozone does not impart a distinctive flavor, color or odor of its own to the water.
While the treatment of water with ozone leaves no chemical residue in the water, this method of disinfection can be rather inefficient and difficult to control. Since ozone is unstable and rapidly disintegrates and further, since it is only slightly soluble in water, it is very important to achieve intimate gas/water contact during treatment. Also, the effect of ozone is not instantaneous and a certain minimum contact time with water is required. All of these factors must be taken into account to be conduct an efficient and reliable ozone treatment.
While the instability of ozone and its low solubility create problems in the disinfection of water, it is these same properties that make the use of ozone of value. Since ozone is unstable, readily disintegrates, and is only slightly soluble in water, water that has been treated with ozone has no residual odor or taste, even though ozone in itself has a characteristic pungent odor.
Since intimate contact between water and ozone is difficult to achieve, it is common practice to dose the water with quantities of ozone in considerable excess of that theoretically required. In addition to being wasteful of ozone these processes are inefficient in that the concentration of ozone may vary considerably between isolated regions of water being treated. Some of the water may not be adequately disinfected, while other water may be bottled with an appreciable excess of ozone. In the first instance, the hazard to health is obvious. In the second instance, the excess ozone may separate from the water during storage and gather at the top of a container. Then, when the container is opened, an initial discharge of ozone takes place that may confront the prospective consumer with a pungent odor. While this occurrence is not in itself harmful or dangerous, it may result in a dissatisfied consumer who mistakenly believes that the water is contaminated or that it has spoiled in storage and transit.
For the above reasons, it is important that the ozonation of water be conducted efficiently and in a manner in which only the required amount of ozone necessary to disinfect the water is used. Obviously, too little ozone can result in inadequate disinfection and excess of ozone can cause customer dissatisfaction.
It has been found, as a practical matter, that it is desirable to add ozone in slight excess of that required to disinfect the water to provide for sterilization of the bottle, the cap and the air space at the top of the bottle. This is particularly important when the water may remain in the bottle for an appreciable length of time before it is used. Quite generally, from about 0.05 to about 0.5 p.m., and more preferably about 0.2 p.m free ozone in the water at the time of bottling will suffice to provide a safe level of residual disinfection.
2. Description of the Prior Art
Methods and apparatus for treating water with ozone as known to the prior art, as, for example, the continuous process disclosed in U.S. Pat. No. 3,448,045. Herein, the importance of operating the ozone generator continuously, without interruption, so that the ozone of uniform quantity and quality. When water is not being treated, rather than discontinue operation of the apparatus, the incoming air supply is discharged to the atmosphere. It was found that if the ozone generator was stopped and started with a varying water demand, the quality of the ozone became inconsistent. The patent also teaches that intimate gas/liquid contact can be achieved by mixing the ozone and water by flowing them through a coiled pipe.